1. Field of the Invention
This invention relates to a prereduction furnace of a smelting reduction facility of iron ore.
2. Description of the Related Arts
A smelting reduction facility of iron ore includes a smelting reduction furnace and a fluidized bed type prereduction furnace. The exhaust gas generated from the smelting reduction furnace is used to fluidize and reduce iron ores in the fluidized bed in the prereduction furnace. The fluidized bed is preferably of a bubbling type that has almost reached technical finality and can prevent the degradation of ore due to preheating and reduction. The prereduction furnace has a distributor therein. The distributor has many nozzles for injecting gas. Iron ores are charged into a prereduction chamber formed above the distributor. Reducing gas from the smelting reduction furnace is introduced into a blowing chamber below the distributor. The reducing gas is blown out into the prereduction chamber above the distributor through the nozzles of the distributor. The reducing gas blown into the prereduction chamber forms a fluidized bed, in which prereduction and preheating of iron ore take place.
With regard to the prereduction furnace, the adhesion of dust contained in the reducing gas to the distributor presents a big problem. The exhaust gas generated from the smelting reduction furnace contains large amounts of dust. The fine particle dust of 10 microns and smaller in the gas cannot be removed by a cyclone or other dust collectors in most cases. The reducing gas containing fine particle dust is introduced into the prereduction furnace without removal of fine-grain dust. The dust, containing Na, K and other alkaline compounds and S in large quantities, is adherent in the reducing gas at temperatures above 900.degree. C. Owing to this adhesion property, the dust introduced into the prereduction furnace adheres to the bottom of the distributor and the inside of the nozzle. In particular, the dust tends to adhere firmly to the inside of the nozzle because the reducing gas introduced into the blowing chamber is contracted when passing through the nozzle, resulting in a flow velocity of gas as high as about 100 m/sec in the nozzle. The adherent dust builds up gradually, preventing the smooth flow of reducing gas and the formation of a proper fluidized bed.